As is commonly known, in a copying machine incorporating a movable document platen, the platen is moved forward and backward or in the F direction and in the R direction. When an optical system scans a document placed on the platen, the platen is moved in the F direction. Meanwhile, the platen is moved in the reverse (R) direction so that it is located in a scanning start position.
In such a copying machine, when scanning a document on the platen, the platen is firstly moved in the R direction from an original position where it is kept on standby to the scanning start position. Secondly, it is moved in the F direction to a scanning end position so as to scan the document. Then, it is moved in the R direction from the scanning end position to the original position.
In this type of a copying machine, for example, a driving device 151 for moving a document platen 152 in the above-mentioned manner is installed under the platen 152 as illustrated in FIG. 27. The driving device 151, for instance, incorporates a driving force transmitting device having gears, latches and solenoids shown in FIG. 28.
In the driving force transmitting device, when moving the platen 152 in the F direction from the scanning start position, a solenoid 153 used for moving the platen 152 in the F direction is actuated. This causes a latch 154 to engage with a clutch brake 156 of a spring clutch 155 for forward movement, whereby the spring clutch 155 is actuated. This allows a driving force passed to an input gear 157 to be transmitted via an output gear 158 to a platen driving gear 159. In consequence, when a rack of the platen 152 engages with the platen driving gear 159, platen 152 is moved in the F direction.
When the platen 152 reaches the scanning end position, a detection switch 160 shown in FIG. 27 detects the arrival of the platen 152 at the scanning end position. Then, the solenoid 153 is turned OFF, while a solenoid 161 used for moving the platen 152 in the R direction is actuated. This causes a latch 162 to engage with a clutch brake 163 of a spring clutch 167 for backward movement, whereby the spring clutch 167 is actuated.
As a result, the driving force passed to the input gear 157 is transmitted via a gear 164, input gear 165, and output gears 166 and 158 to the platen driving gear 159. And then, the platen 152 is moved in the R direction from the scanning end position to the original position. In the case of performing copying operations subsequently, the platen 152 is moved in the R direction to the scanning start position through the original position.
In such a copying machine incorporating a movable document platen, usually, there is not need to provide means for moving the optical system as the platen 152 is moved. Accordingly, it is possible to simplify the structure of the copying machine, and thereby resulting in a smaller copying machine. Thus, such a configuration is often adopted into inexpensive models.
However, with the above-mentioned conventional configuration, in order to achieve reciprocating movement of the platen 152, the spring clutch 155 and solenoid 153 for forward movement, and the spring clutch 167 and solenoid 161 for backward movement must be provided. In addition, in order to detect the arrival of the platen 152 at the scanning end position, the detection switch 160 is needed to be supplied.
Therefore, with this configuration, an increased number of components are necessary in order to reciprocate the platen 152. Consequently, the proportion of these components to the total cost becomes greater, causing an increase in the cost of manufacturing the copying machine.